A malfunction in a DNA processing machine led to the scrambling of samples from 11 Denver police burglary cases, officials acknowledged Friday. It took more than two years for the department to discover the errors.

As a result of the mix-up, prosecutors are dismissing burglary cases against four people, three of whom had already pleaded guilty.

All four people had confessed to at least one burglary, but the DNA error meant they were charged with the wrong ones, Denver district attorney spokeswoman Lynn Kimbrough said.

The problem caused evidence from one case to be tied to another. Authorities have since sorted out the samples, but prosecutors won’t refile charges against the four people because the statute of limitations has expired. Two of the dismissed cases were against juveniles.

They will file charges in a fifth burglary case, against an adult who is already jailed on unrelated crimes in Adams County, Kimbrough said.

The mistake happened after an $80,000 DNA processing machine “froze” while running a tray of 19 DNA samples on June 13, 2011. An analyst in the city’s crime lab then called the manufacturer, which supplied directions for putting the samples back onto the machine in the right sequence. Either the directions were incorrect or the analyst misinterpreted them, and the samples were replaced in the wrong order, said Lt. Matt Murray, the department’s chief of staff.

The crime lab didn’t suspect the possibility of an error until after the machine froze for a second time on Nov. 22, 2013, and an analyst again requested directions from the manufacturer. The analyst became concerned because the directions seemed different the second time.

Further review over the next month uncovered the earlier mix-up, Murray said.

“The samples were returned to the tray out of sequence,” Murray said at a news conference to announce the error. “None of the DNA was compromised; it was merely associated with the wrong case when we were done.”

Lab officials notified the police department of the problem late Thursday, he said. District Attorney Mitch Morrissey was notified Friday afternoon.

Though Murray said the department was still trying to learn the extent of the impact on criminal cases, he said DNA from eight burglary cases didn’t end up being used in the criminal investigations.

“This is regarding one run, on one day,” Murray said, adding that the $36 million state-of-the-art lab handles more than 2,300 DNA samples a year. “DNA is part of the process. It’s often touted as the end-all-be-all in all criminal cases, and that’s just not true.”

Kimbrough described the problem as “very limited in scope.”

But criminal defense attorneys and experts said the error could have far-reaching implications in court. Defense attorneys might start challenging the accuracy of DNA evidence in cases that had nothing to do with the mix-up because it revealed that “even if the testing is done right, the storage of the information might be mismanaged,” defense attorney Dan Recht said.

“The kind of attack you’re going to now see is that the jury should be skeptical of all DNA results because you never know if the information itself was stored correctly by DPD. This is damaging to law enforcement and damaging to Denver prosecutors.”

The mistake is also a reminder that DNA evidence is not flawless, even though it can be powerful for juries, especially in property crimes cases where there are often no witnesses, said Phillip Danielson, a professor of molecular biology at the University of Denver. He said luck, rather than sophisticated quality control systems, led to the discovery of the problem.

“Had the instrument not broken down a second time, they would have continued to think those samples processed in 2011 were correctly processed,” Danielson said. “Incidents of cross-contamination or sample mix-ups can occur and not be detected by the quality- control systems labs currently have in place.”

The department will continue to investigate how the error happened, and the city and district attorney’s office will notify defendants in the applicable cases, Murray said.

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